1. Technical Field
The present invention relates to a technology for realizing the sound image movement accompanying the Doppler effect.
2. Related Art
A technique is known in which music sound signals on the left and right signal lines are delayed in time and adjusted in amplitude to cause a time delay and an amplitude difference between the left and right signal lines, thereby auditorily providing a sense of direction and distance perspective to music sounds to create a sense of sound image panning.
Meanwhile, if a sound source and a listener listening to a music sound generated from the sound source are moving relative to each other (for example, a sound source is moving at a predetermined velocity while the listener is standing still), the Doppler effect occurs in accordance with the relative movement. However, if a sound image movement is expressed solely by the time difference and the amplitude difference between the left and right signal lines as described above, the Doppler effect cannot be represented realistically, thereby causing a problem of poor sound quality.
In order to solve this problem, a technique was proposed as disclosed in Japanese Publication of Unexamined Patent Application No. Hei 06-327100, for example. In the disclosed technique, the frequency of a sound signal outputted from a frequency-variable sound source is varied in accordance with a manner by which a sound image moves, and the sound signal generated from the frequency-variable sound source and separated into the left and right channels is outputted as delayed in accordance with that movement, thereby rendering the Doppler effect.
The synchronous reproduction of moving picture and music sound as with video games requires to make synchronization between the sound source movement represented in the moving picture and the sound image movement. For the technique disclosed in Japanese Publication of Unexamined Patent Application No. Hei 06-327100, in order to realize the sound image movement accompanying the Doppler effect, a condition and manner by which the sound source moves must be grasped by reproducing the above-mentioned moving picture on a frame by frame basis, and the frequency of the sound signal outputted from the above-mentioned frequency-variable sound source must be varied in accordance with the moving condition, thus requiring cumbersome tasks. Another problem is that, because the sound source moving condition must be visually checked, it is difficult to realize the sound image movement that correctly synchronizes with the sound source moving condition represented in the moving pictures.